Effects of substrate composition on Apache trout fry emergence

Artificial substrates were used under laboratory conditions to assess the p otential effects of fine sediment (< 2 mm) on a native southwestern (USA) s almonid. Apache trout (Oncorhynchus apache). Asynchronous, complementary fi eld assessment of stream substrate composition was made in the White Mounta ins of east-central Arizona, the native range of Apache trout. Laboratory s tudies suggested that fry emergence was significantly reduced at 25% or gre ater by weight of fine sediments. Mean fine content of substrates in stream s in the White Mountains ranged from 8 to 43% and averaged about 24%. Based on laboratory and field data, streams in the White Mountains region are ap proaching the threshold that could dramatically limit reproductive success of Apache trout. Further, a significantly greater content of optimum spawni ng substrate (8-32 mm) was estimated in streams emanating from the Fort Apa che Indian Reservation than those in Apache Sitgreaves National Forest.